MDEV-22990 Threadpool : Optimize network/named pipe IO for Windows

This patch reduces the overhead of system calls prior to a query, for
threadpool.  Previously, 3 system calls were done

1. WSARecv() to get notification of input data from client, asynchronous
equivalent of select() in one-thread-per-connection

2. recv(4 bytes) - reading packet header length
3. recv(packet payload)

Now there will be usually, just WSARecv(), which pre-reads user data into
a buffer, so we spared 2 syscalls

Profiler shows the most expensive call WSARecv(16%CPU) becomes 4% CPU,
after the patch, benchmark results (network heavy ones like point-select)
improve by ~20%

The buffer management was rather carefully done to keep
buffers together, as Windows would keeps the pages pinned
in memory for the duration of async calls.
At most 1MB memory is used for the buffers, and overhead per-connection is
only 256 bytes, which should cover most of the uses.

SSL does not yet use the optmization, so far it does not properly use
VIO for reads and writes. Neither one-thread-per-connection would get any
benefit, but that should be fine, it is not even default on Windows.

include/violite.h

@@ -278,6 +278,7 @@ struct st_vio
 #ifdef _WIN32
   HANDLE hPipe;
   OVERLAPPED overlapped;
+  void *tp_ctx; /* threadpool context */
 #endif
 };
 #endif /* vio_violite_h_ */

sql/CMakeLists.txt

@@ -171,7 +171,7 @@ IF ((CMAKE_SYSTEM_NAME MATCHES "Linux" OR
     AND (NOT DISABLE_THREADPOOL))
  ADD_DEFINITIONS(-DHAVE_POOL_OF_THREADS)
  IF(WIN32)
-   SET(SQL_SOURCE ${SQL_SOURCE} threadpool_win.cc)
+   SET(SQL_SOURCE ${SQL_SOURCE} threadpool_win.cc threadpool_winsockets.cc threadpool_winsockets.h)
  ENDIF()
  SET(SQL_SOURCE ${SQL_SOURCE} threadpool_generic.cc)
  SET(SQL_SOURCE ${SQL_SOURCE} threadpool_common.cc)

sql/threadpool.h

@@ -37,6 +37,8 @@ extern uint threadpool_mode; /* Thread pool implementation , windows or generic
 #define DEFAULT_THREADPOOL_STALL_LIMIT 500U
 
 struct TP_connection;
+struct st_vio;
+
 extern void tp_callback(TP_connection *c);
 extern void tp_timeout_handler(TP_connection *c);
 
@@ -115,7 +117,7 @@ struct TP_connection
 
   virtual void wait_begin(int type)= 0;
   virtual void wait_end() = 0;
-
+  IF_WIN(virtual,) void init_vio(st_vio *){};
 };
 
 
@@ -136,6 +138,7 @@ struct TP_pool
 };
 
 #ifdef _WIN32
+
 struct TP_pool_win:TP_pool
 {
   TP_pool_win(); 

sql/threadpool_common.cc

@@ -28,6 +28,10 @@
 #include "wsrep_trans_observer.h"
 #endif /* WITH_WSREP */
 
+#ifdef _WIN32
+#include "threadpool_winsockets.h"
+#endif
+
 /* Threadpool parameters */
 
 uint threadpool_min_threads;
@@ -48,7 +52,7 @@ TP_STATISTICS tp_stats;
 
 static void  threadpool_remove_connection(THD *thd);
 static int   threadpool_process_request(THD *thd);
-static THD*  threadpool_add_connection(CONNECT *connect, void *scheduler_data);
+static THD*  threadpool_add_connection(CONNECT *connect, TP_connection *c);
 
 extern bool do_command(THD*);
 
@@ -221,7 +225,7 @@ void tp_callback(TP_connection *c)
 }
 
 
-static THD* threadpool_add_connection(CONNECT *connect, void *scheduler_data)
+static THD *threadpool_add_connection(CONNECT *connect, TP_connection *c)
 {
   THD *thd= NULL;
 
@@ -243,9 +247,10 @@ static THD* threadpool_add_connection(CONNECT *connect, void *scheduler_data)
     return NULL;
   }
   delete connect;
+
   server_threads.insert(thd);
   thd->set_mysys_var(mysys_var);
-  thd->event_scheduler.data= scheduler_data;
+  thd->event_scheduler.data = c;
 
   /* Login. */
   thread_attach(thd);
@@ -260,6 +265,8 @@ static THD* threadpool_add_connection(CONNECT *connect, void *scheduler_data)
   if (thd_prepare_connection(thd))
     goto end;
 
+  c->init_vio(thd->net.vio);
+
   /*
     Check if THD is ok, as prepare_new_connection_state()
     can fail, for example if init command failed.
@@ -397,6 +404,9 @@ static bool tp_init()
     pool= 0;
     return true;
   }
+#ifdef _WIN32
+  init_win_aio_buffers(max_connections);
+#endif
   return false;
 }
 
@@ -484,6 +494,9 @@ static void tp_wait_end(THD *thd)
 static void tp_end()
 {
   delete pool;
+#ifdef _WIN32
+  destroy_win_aio_buffers();
+#endif
 }
 
 static void tp_post_kill_notification(THD *thd)

sql/threadpool_generic.cc

@@ -29,8 +29,8 @@
 #include <sql_plist.h>
 #include <threadpool.h>
 #include <algorithm>
-
-#ifdef HAVE_IOCP
+#ifdef _WIN32
+#include "threadpool_winsockets.h"
 #define OPTIONAL_IO_POLL_READ_PARAM this
 #else 
 #define OPTIONAL_IO_POLL_READ_PARAM 0
@@ -348,7 +348,7 @@ static void* native_event_get_userdata(native_event *event)
   return event->portev_user;
 }
 
-#elif defined(HAVE_IOCP)
+#elif defined(_WIN32)
 
 
 static TP_file_handle io_poll_create()
@@ -359,29 +359,8 @@ static TP_file_handle io_poll_create()
 
 int io_poll_start_read(TP_file_handle pollfd, TP_file_handle fd, void *, void *opt)
 {
-  static char c;
-  TP_connection_generic *con= (TP_connection_generic *)opt;
-  OVERLAPPED *overlapped= &con->overlapped;
-  if (con->vio_type == VIO_TYPE_NAMEDPIPE)
-  {
-    if (ReadFile(fd, &c, 0, NULL, overlapped))
-      return 0;
-  }
-  else
-  {
-    WSABUF buf;
-    buf.buf= &c;
-    buf.len= 0;
-    DWORD flags=0;
-
-    if (WSARecv((SOCKET)fd, &buf, 1,NULL, &flags,overlapped, NULL) == 0)
-      return 0;
-  }
-
-  if (GetLastError() == ERROR_IO_PENDING)
-    return 0;
-
-  return 1;
+  auto c= (TP_connection_generic *) opt;
+  return (int) c->win_sock.begin_read();
 }
 
 
@@ -401,20 +380,33 @@ int io_poll_disassociate_fd(TP_file_handle pollfd, TP_file_handle fd)
 }
 
 
-int io_poll_wait(TP_file_handle pollfd, native_event *events, int maxevents, int timeout_ms)
+static void *native_event_get_userdata(native_event *event)
 {
-  ULONG n;
-  BOOL ok = GetQueuedCompletionStatusEx(pollfd, events, 
-     maxevents, &n, timeout_ms, FALSE);
-
-  return ok ? (int)n : -1;
+  return (void *) event->lpCompletionKey;
 }
 
-
-static void* native_event_get_userdata(native_event *event)
+int io_poll_wait(TP_file_handle pollfd, native_event *events, int maxevents,
+                 int timeout_ms)
 {
-  return (void *)event->lpCompletionKey;
+  ULONG n;
+  if (!GetQueuedCompletionStatusEx(pollfd, events, maxevents, &n, timeout_ms, FALSE))
+    return -1;
+
+  /* Update win_sock with number of bytes read.*/
+  for (ULONG i= 0; i < n; i++)
+  {
+    auto ev= &events[i];
+    auto c= (TP_connection_generic *) native_event_get_userdata(ev);
+    /* null userdata zero means shutdown (see PostQueuedCompletionStatus() usage*/
+    if (c)
+    {
+      c->win_sock.end_read(ev->dwNumberOfBytesTransferred, 0);
+    }
+  }
+
+  return (int) n;
 }
+
 #endif
 
 
@@ -969,7 +961,7 @@ void thread_group_destroy(thread_group_t *thread_group)
     io_poll_close(thread_group->pollfd);
     thread_group->pollfd= INVALID_HANDLE_VALUE;
   }
-#ifndef HAVE_IOCP
+#ifndef _WIN32
   for(int i=0; i < 2; i++)
   {
     if(thread_group->shutdown_pipe[i] != -1)
@@ -1013,7 +1005,7 @@ static int wake_thread(thread_group_t *thread_group,bool due_to_stall)
 */
 static int wake_listener(thread_group_t *thread_group)
 {
-#ifndef HAVE_IOCP
+#ifndef _WIN32
   if (pipe(thread_group->shutdown_pipe))
   {
     return -1;
@@ -1354,9 +1346,6 @@ TP_connection_generic::TP_connection_generic(CONNECT *c):
   abs_wait_timeout(ULONGLONG_MAX),
   bound_to_poll_descriptor(false),
   waiting(false)
-#ifdef HAVE_IOCP
-, overlapped()
-#endif
 {
   DBUG_ASSERT(c->vio_type != VIO_CLOSED);
 

sql/threadpool_generic.h

@@ -23,6 +23,7 @@
 
 #ifdef _WIN32
 #include <windows.h>
+#include "threadpool_winsockets.h"
 /* AIX may define this, too ?*/
 #define HAVE_IOCP 
 #endif
@@ -75,11 +76,11 @@ struct TP_connection_generic :public TP_connection
   TP_connection_generic(CONNECT* c);
   ~TP_connection_generic();
 
-  virtual int init() { return 0; };
-  virtual void set_io_timeout(int sec);
-  virtual int  start_io();
-  virtual void wait_begin(int type);
-  virtual void wait_end();
+  int init() override { return 0; }
+  void set_io_timeout(int sec) override;
+  int  start_io() override;
+  void wait_begin(int type) override;
+  void wait_end() override;
 
   thread_group_t* thread_group;
   TP_connection_generic* next_in_queue;
@@ -89,12 +90,13 @@ struct TP_connection_generic :public TP_connection
   TP_file_handle fd;
   bool bound_to_poll_descriptor;
   int waiting;
-#ifdef HAVE_IOCP
-  OVERLAPPED overlapped;
-#endif
+
 #ifdef _WIN32
-  enum_vio_type vio_type;
+  win_aiosocket win_sock{};
+  void init_vio(st_vio *vio) override
+  { win_sock.init(vio);}
 #endif
+
 };